Fix and document CompositeUriComponentsContributor#hasContributors()

Prior to this commit, the hasContributors() method incorrectly returned
false if contributors had been configured.

This commit fixes the logic in hasContributors() and documents it.

Closes #27271

spring-web/src/main/java/org/springframework/web/method/support/CompositeUriComponentsContributor.java

 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -31,8 +31,8 @@ import org.springframework.web.util.UriComponentsBuilder;
 
 /**
  * A {@link UriComponentsContributor} containing a list of other contributors
- * to delegate and also encapsulating a specific {@link ConversionService} to
- * use for formatting method argument values to Strings.
+ * to delegate to and also encapsulating a specific {@link ConversionService} to
+ * use for formatting method argument values as Strings.
  *
  * @author Rossen Stoyanchev
  * @author Juergen Hoeller
@@ -52,7 +52,7 @@ public class CompositeUriComponentsContributor implements UriComponentsContribut
 	 * {@code HandlerMethodArgumentResolvers} in {@code RequestMappingHandlerAdapter}
 	 * and provide that to this constructor.
 	 * @param contributors a collection of {@link UriComponentsContributor}
-	 * or {@link HandlerMethodArgumentResolver HandlerMethodArgumentResolvers}.
+	 * or {@link HandlerMethodArgumentResolver HandlerMethodArgumentResolvers}
 	 */
 	public CompositeUriComponentsContributor(UriComponentsContributor... contributors) {
 		this.contributors = Arrays.asList((Object[]) contributors);
@@ -66,7 +66,7 @@ public class CompositeUriComponentsContributor implements UriComponentsContribut
 	 * {@code HandlerMethodArgumentResolvers} in {@code RequestMappingHandlerAdapter}
 	 * and provide that to this constructor.
 	 * @param contributors a collection of {@link UriComponentsContributor}
-	 * or {@link HandlerMethodArgumentResolver HandlerMethodArgumentResolvers}.
+	 * or {@link HandlerMethodArgumentResolver HandlerMethodArgumentResolvers}
 	 */
 	public CompositeUriComponentsContributor(Collection<?> contributors) {
 		this(contributors, null);
@@ -82,7 +82,7 @@ public class CompositeUriComponentsContributor implements UriComponentsContribut
 	 * {@link org.springframework.format.support.DefaultFormattingConversionService}
 	 * will be used by default.
 	 * @param contributors a collection of {@link UriComponentsContributor}
-	 * or {@link HandlerMethodArgumentResolver HandlerMethodArgumentResolvers}.
+	 * or {@link HandlerMethodArgumentResolver HandlerMethodArgumentResolvers}
 	 * @param cs a ConversionService to use when method argument values
 	 * need to be formatted as Strings before being added to the URI
 	 */
@@ -91,9 +91,14 @@ public class CompositeUriComponentsContributor implements UriComponentsContribut
 		this.conversionService = (cs != null ? cs : new DefaultFormattingConversionService());
 	}
 
-
+	/**
+	 * Determine if this {@code CompositeUriComponentsContributor} has any
+	 * contributors.
+	 * @return {@code true} if this {@code CompositeUriComponentsContributor}
+	 * was created with contributors to delegate to
+	 */
 	public boolean hasContributors() {
-		return this.contributors.isEmpty();
+		return !this.contributors.isEmpty();
 	}
 
 	@Override
@@ -139,7 +144,7 @@ public class CompositeUriComponentsContributor implements UriComponentsContribut
 	public void contributeMethodArgument(MethodParameter parameter, Object value, UriComponentsBuilder builder,
 			Map<String, Object> uriVariables) {
 
-		this.contributeMethodArgument(parameter, value, builder, uriVariables, this.conversionService);
+		contributeMethodArgument(parameter, value, builder, uriVariables, this.conversionService);
 	}
 
 }

spring-web/src/test/java/org/springframework/web/method/support/CompositeUriComponentsContributorTests.java

 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -32,30 +32,33 @@ import org.springframework.web.method.annotation.RequestParamMethodArgumentResol
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
- * Unit tests for
- * {@link org.springframework.web.method.support.CompositeUriComponentsContributor}.
+ * Unit tests for {@link CompositeUriComponentsContributor}.
  *
  * @author Rossen Stoyanchev
+ * @author Sam Brannen
  */
-public class CompositeUriComponentsContributorTests {
-
+class CompositeUriComponentsContributorTests {
 
 	@Test
-	public void supportsParameter() {
-
+	void supportsParameter() {
 		List<HandlerMethodArgumentResolver> resolvers = new ArrayList<>();
 		resolvers.add(new RequestParamMethodArgumentResolver(false));
 		resolvers.add(new RequestHeaderMethodArgumentResolver(null));
 		resolvers.add(new RequestParamMethodArgumentResolver(true));
 
-		Method method = ClassUtils.getMethod(this.getClass(), "handleRequest", String.class, String.class, String.class);
-
 		CompositeUriComponentsContributor contributor = new CompositeUriComponentsContributor(resolvers);
+		Method method = ClassUtils.getMethod(this.getClass(), "handleRequest", String.class, String.class, String.class);
 		assertThat(contributor.supportsParameter(new MethodParameter(method, 0))).isTrue();
 		assertThat(contributor.supportsParameter(new MethodParameter(method, 1))).isTrue();
 		assertThat(contributor.supportsParameter(new MethodParameter(method, 2))).isFalse();
 	}
 
+	@Test
+	void hasContributors() {
+		assertThat(new CompositeUriComponentsContributor().hasContributors()).isFalse();
+		assertThat(new CompositeUriComponentsContributor(new RequestParamMethodArgumentResolver(true)).hasContributors()).isTrue();
+	}
+
 
 	public void handleRequest(@RequestParam String p1, String p2, @RequestHeader String h) {
 	}